Definitive lumber grade charts are available online at SouthernPine.com, SPIB.org, WWPA.org and Lowes.com as of 2015. Types of lumber range from residential hardwood and softwood to stadium lumber and mining lumber.
Southern Pine offers the most comprehensive grading chart, which organizes the wood by dimension, stress rating, wood type and whether the wood is visually graded by a person or graded by a machine. The WWPA sorts its grades in similar fashion.
The Lowe's grades are simpler and deal in hardwood and softwood grades that are oriented more toward residential consumers.
The Southern Pine Inspection Bureau goes into detail about how to read lumber grade stamps. There are different marks for different grades, with the simplest stamp for general boards.